Ventricular fibrillation (VF) is a life-threatening condition in which the cardiac cells in one or both ventricles of the heart of a patient contract in a random and uncoordinated fashion. During an episode of VF, the heart is unable to pump blood. VF rarely terminates spontaneously. Patients at risk of VF may receive an implantable medical device (IMD), such as a pacemaker-defibrillator, that can detect VF and apply defibrillation therapy to terminate the episode. VF will cause death in a short period of time unless terminated.
Many patients that are at risk of developing VF are also at risk of experiencing tachycardia. Tachycardia is an abnormal heart rhythm characterized by rapid activation of one or more chambers of the heart. Tachycardia is often qualified by the locus of origin: a tachycardia that originates in the ventricles of the heart is called a ventricular tachycardia (VT) and a tachycardia that originates in the atria of the heart is called an atrial tachycardia (AT) or a supraventricular tachycardia (SVT). Some VTs, if untreated, may accelerate into VF, in which the pumping ability of the heart is seriously impaired.
In some patients, VT or AT may respond well to antitachycardia pacing (ATP), in which small electric stimulations from an implantable pulse generator (IPG) in an IMD disrupt the propagation of electrical signals that cause the tachycardia. The IMD may be programmed to administer several forms of ATP therapies, and may apply one ATP therapy after another until the tachycardia terminates. Tachycardia therapies may also include the application of a higher voltage cardioversion shock to terminate the tachycardia.
A conventional IMD that includes the capability to treat VF also includes the capability to treat VT with ATP and/or with a shock. When the IMD is implanted, however, all VF- and VT-related functions are “off” to avoid inadvertent therapy delivery during device manipulation that may accompany implantation. At the end of the IMD implant procedure, a clinician such as an electrophysiologist, activates the detection functionality and the therapies that are believed will be beneficial or appropriate to the patient. The clinician may use a programmer that communicates wirelessly with the IMD to program the IMD and activate the therapies. With a conventional IMD and a conventional programmer, each therapy is turned “on” individually, i.e., a clinician sets each therapy to active status on a therapy-by-therapy basis.